Recently, a size of a wafer has become larger in diameter and, simultaneously, a single wafer processing type has become a main stream of a semiconductor processing system in the place of a batch processing type.
A single wafer processing type of a semiconductor processing system in an earlier technology comprises gas injecting means for injecting a process gas to be contributed to a reaction into a reactor, susceptor means for supporting a wafer in the reactor, energy supplying means for exciting and reacting the process gas injected in the reactor, and gas pumping means for pumping out the process gas from the reactor. In this system, the process gas is injected downward onto the wafer supported in the reactor, and then, thermal or plasma energy is supplied to the process gas to excite and react the process gas, in order to repeatedly perform a film deposition process for depositing a film corresponding to a composition of the process gas on the wafer or an etching process.
In such a process, it is required to reduce the number of particles of a reaction product attached on the wafer in view of a large scale integration of semiconductor devise. For example, the number thereof is required to be less than 10 particles, each particle having more than 0.1 .mu.m in diameter, on a wafer having 200 mm in diameter.
In general, a part of the process gas is not contributed to a film deposition and a part of the reaction product is not deposited on a wafer. In the semiconductor processing system described above, such a process gas and such a residual reaction product should be pumped out from a reaction region of the reactor by following to a pumped gas flow. However, the residual reaction product is deposited on a wall of the reactor during the residual reaction product is pumped out from the reactor, and as a result, when a film deposition is repeatedly performed, the residual reaction product deposited on the wall of the reactor is separated and floated and is then attached on the wafer.
As an example, in a chemical vapor deposition (CVD) system which serves to form a silicon oxide film on a wafer by flowing a gas mixture as a process gas of tetraethoxysilane (Si(OC.sub.2 H.sub.5).sub.4) (TEOS) and ozone gas over a surface of the wafer, a large quantity of a silicon oxide film as a residual reaction product is deposited inside a reactor thereof.
Also, as another example, in a film deposition processing system which serves to form a tungsten film by tungsten reduction reaction by injecting WF.sub.6 gas, SiH.sub.4 gas and H.sub.2 gas, such a metallic film is deposited on a wall of a reactor thereof other than a surface of a wafer and is then separated from the wall, and particles thereof is floated in the reactor and is then attached on the wafer so as to contaminate the wafer.
Thus, in order to remove a reaction product deposited inside a reactor, a wafer is unloaded from the reactor after the wafer is completely processed and then, a periodical cleaning of the reactor is manually done, or a chemical cleaning is done by introducing a chemically reactive gas into the reactor to change a film of the reaction product deposited inside the reactor into a gas condition or by use of an excited fluoric plasma gas.
Meanwhile, the capacity of throughput in a processing system can be represented by the product of the working time of the system and the throughput per unit time.
In a single wafer processing type of the semiconductor processing system described above, a replacement of expendable supplies of the system and a cleaning inside the reactor must be done during the system is stopped, and thus, in order to improve the capacity of throughput of the system, it is required to improve the throughput during the working time of the system and to reduce the non working time thereof.
In general, the deposition rate is increased in order to improve the throughput in the working time. However, for example, when an insulating film is deposited by plasma excitation, the deposition rate is required to be more than 500 nm/min.
In order to achieve such a high deposition rate, it is important to flow a gas to be contributed to a reaction uniformly over a wafer.
A single wafer processing type of a semiconductor processing system disclosed in Japanese Patent Laying-Open No. Heisei 6 (1994)-13368 (corresponding to U.S. Ser. No. 944492 ) comprises a plasma self cleaning mechanism and gas flow adjusting means for flowing a process gas from a central part of a wafer to a circumference thereof.
The semiconductor processing system of Japanese Patent Laying-Open No. Heisei 6(1994)-13368 is a plasma excitation vapor deposition processing system, and the gas flow adjusting means thereof comprise a gas flow adjusting plate having exhaust holes arranged annularly thereon and are provided below a position of the wafer placed in the reactor so as to locate the annular arrangement of the exhaust holes of the gas flow adjusting plate around and bellow the wafer. The wafer is supported by a susceptor. A manifold is located above the wafer, and a gas is injected and directed to the wafer through many holes provided in the manifold. The gas directed to the wafer is excited as plasma excitation between plasma generating electrodes comprising of the manifold (as a RF electrode) and the susceptor (as a ground electrode), and the gas is changed into an active condition and is reacted on the wafer supported by the susceptor. After the wafer is processed, the gas is pumped out from the reactor through the exhaust holes arranged annularly on the gas flow adjusting plate provided around and below the wafer position and through an annular channel communicated with those exhaust holes.
After a film deposition is completed, a fluoric gas is introduced into the reactor and is then activated by plasma energy so as to generate an active species of the fluoric gas, and thereby a reaction product attached inside the reactor is removed (plasma cleaning
In the system of Japanese Patent Laying-Open No. Heisei 6(1994)-13368, the exhaust holes are annularly arranged on the gas flow adjusting plate at spaces between them, and due to such an arrangement, even though the activated fluoric gas comes into the annular channel, the activated fluoric gas can not be carried well through the whole space inside the channel and as a result, a reaction product attached inside the channel can not be removed completely.
Thus, when a wafer is successively processed, a residual reaction product inside the channel is floated so as to contaminate the wafer.
A gas flow rate injected into a reactor depends on a nature of a film to be deposited and a condition of a film deposition.
In general, in a single wafer processing type of a semiconductor processing system, when the gas flow rate is small, a uniform gas flow over a wafer is achieved by additionally introducing a carrier gas (which is not contributed to a reaction) into the reactor.
In the system of Japanese Patent Laying-Open No. Heisei 6(1994)-13368, when a silicon dioxide film is deposited on a wafer by use of plasma energy, helium gas as an inert gas (a carrier gas) is additionally introduced into the reactor (900 sccm of helium gas against 600 sccm of oxygen gas). That is, 1500 sccm of gas is totally introduced into the reactor to achieve a uniform gas flow over the wafer.
However, when a carrier gas is additionally introduced, the concentration of a process gas and the deposition rate are reduced, and as a result, the capacity of processing a wafer in the system is reduced.